Methods for fabricating residue-free contact openings

ABSTRACT

A two-step via cleaning process that removes metal polymer and oxide polymer residues from a via with substantially no damage to the via or underlying structures on a semiconductor substrate. The two-step cleaning process comprises first subjecting the residue layer to a nitric acid dip that removes the metal polymer component to expose the oxide polymer component. The oxide polymer component is then subjected to a phosphoric acid dip that removes the oxide polymer component. The oxide polymer and metal polymer residues may also be removed during the fabrication of the via by removing them directly after their respective formations.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 09/035,497,filed Mar. 5, 1998, now U.S. Pat. No. 6,576,547, issued Jun. 10, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fabricating a via employed in anintegrated circuit which is substantially free of metal polymer andoxide polymer residues. More particularly, the present invention relatesto a two-step via cleaning process which removes metal polymer and oxidepolymer residues from a via with substantially no damage to the via orunderlying structures carried on a semiconductor substrate.

2. State of the Art

Higher performance, lower cost, increased miniaturization of components,and greater packaging density of integrated circuits are ongoing goalsof the computer industry. One commonly used technique in the fabricationof integrated circuits involves stacking of multiple layers of activeand passive components one atop another to allow for multilevelelectrical interconnection between devices formed on each of theselayers. This multilevel electrical interconnection is generally achievedwith a plurality of metal-filled vias (“contacts”) extending throughdielectric layers which separate the component layers from one another.These vias are generally formed by anisotropically etching through eachdielectric layer by etching methods known in the industry, such asplasma etching and reactive ion etching. A fluorinated gas, such as CF₄,CHF₃, C₂F₆, CH₂F₂, SF₆, or other freons, and mixtures thereof, incombination with a carrier gas, such as Ar, He, Ne, Kr, O₂, or mixturesthereof, is usually used as the etching gas for these etching methods. Aproblem with such etching methods is that at least one layer of residueforms in the vias as a result of the etching process.

An exemplary method for forming a via through a dielectric layer isillustrated in FIGS. 11-14. It should be understood that the figurespresented in conjunction with this description are not meant to beactual cross-sectional views of any particular portion of an actualsemiconductor device, but are merely idealized representations which areemployed to more clearly and fully depict the process of this typicalmethod than would otherwise be possible.

FIG. 11 illustrates an intermediate structure 200 comprising asemiconductor substrate bearing a dielectric or insulating layer 202(such as an oxide) having a metal-containing trace or pad 204 ofaluminum, aluminum alloys, titanium, titanium/tungsten alloys,molybdenum, or the like, formed thereon. The term “semiconductorsubstrate” is used herein to denote any solid semiconductor surface,such as is provided by a silicon or gallium arsenide wafer, or a layerof such material formed on glass, ceramic, sapphire, or other supportingcarrier, as known in the art, and includes such semiconductor surfacesbearing an insulating layer thereon. A barrier layer 206 (such astitanium nitride) extends over the metal-containing trace or pad 204,and an interlayer dielectric 208 (such as silicon dioxide) is disposedover the barrier layer 206. As shown in FIG. 12, the interlayerdielectric 208 is masked with a resist material 212, which is thenpatterned to define a via location. A partial via 214 is thenselectively etched with a fluorinated gas down to the barrier layer 206,which acts as an etch stop. The etching of the partial via 214 resultsin a first residue layer 216 of a carbon-fluorine-based,polymer-containing residue of the interlayer dielectric 208 (“oxidepolymer”) coating the sidewall 218 of the partial via 214, as shown inFIG. 13. The barrier layer 206 at the bottom of partial via 214 is thenetched to expose the metal-containing trace or pad 204 and form a fullvia 222, as shown in FIG. 14. However, due to the variation in thethickness of the interlayer dielectric 208 from the center of the waferto the edge (usually between 4000 and 5000 Å), an oxide over-etch isapplied, such that the via will usually extend through the barrier layer206 and into the metal-containing trace or pad 204. When the barrierlayer 206 and metal-containing trace or pad 204 are etched, a secondresidue layer 224 (“metal polymer”) of a carbon-fluorine-based polymerincluding metal etched from the metal-containing trace or pad 204, aswell as any metal components in the barrier layer 206, such as thetitanium in a titanium nitride barrier layer, is formed over the firstresidue layer 216 and the exposed surface 226 of the metal-containingtrace or pad 204, also shown in FIG. 14. It is, of course, understoodthat a single etch could be performed to expose the metal-containingtrace or pad 204, which etch would result in a single residue layer.However, even if a single etch were performed, the single residue layerwould still have a portion of the residue layer adjacent the viasidewall 218 containing primarily oxide polymer and a portion adjacentthe via aperture and the bottom of the via containing primarily metalpolymer.

Residue layers, such as first residue layer 216 and second residue layer224, which coat the full via 222, are very difficult to remove. Theseresidue layers may be removed by dipping the structure in a 35° C.phosphoric acid solution, preferably about a 20:1 ratio (volume of waterto volume of acid) solution, for about 90 seconds. Although thistechnique is effective in removing most of the residue layers, theresidue layers are still not completely removed. The portion of theresidue layers still remaining after the phosphoric acid dip adverselyaffects the conductivity of contacts subsequently formed in the full via222. It is noted that, although extending the residence time of thesemiconductor substrate structure in the phosphoric acid willeffectively remove all of the residue layer(s), the increased residencetime also results in damage to the metal-containing trace or pad 204.

Thus, it can be appreciated that it would be advantageous to develop atechnique to clean substantially all of the residue layer(s) from asemiconductor via without substantial damage to the metal-containingtrace or pad while using commercially available, widely practicesemiconductor device fabrication techniques.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a two-step via cleaning process thatremoves metal polymer and oxide polymer residues from a via in adielectric layer with substantially no damage to the via or underlyingstructures. One embodiment of the present invention relates to theremoval of the metal polymer and oxide polymer residues after theformation of the via. The via is formed through a dielectric layer and abarrier layer that are disposed over a metal-containing trace, pad, orother circuit element, wherein the metal-containing trace, pad, or othercircuit element is disposed on a semiconductor substrate over theaforementioned oxide or other insulator. When such a via is formed, thesidewall of the via is coated with a residue layer. The residue layergenerally has two distinct components: an oxide polymer layer and ametal polymer layer.

The two-step cleaning process of the present invention completelyremoves both components of the residue layer. The residue layer is firstsubjected to a nitric acid dip to remove the metal polymer layer andexpose the oxide polymer layer. The oxide polymer layer is thensubjected to a phosphoric acid solution dip to remove the oxide polymerlayer. It has also been found that fluorine-containing mixtures, such ashydrofluoric acid (HF) and ammonium fluoride (NH₄F), may be used in lieuof the phosphoric acid solution or mixed with phosphoric acid forremoval of the oxide polymer layer.

The oxide polymer and metal polymer layers may also be removed duringthe fabrication of the via, between the formation of the partial via andits extension to the underlying trace and after the full via formation,respectively. A partial via, or first via portion, is formed by maskingthe dielectric layer and etching through to the barrier layer (etchstop), which forms the oxide polymer residue on the walls of the partialvia. The oxide polymer residue is then subjected to a phosphoric acidsolution dip, which removes the oxide polymer residue. The barrier layeris then etched to extend the via in a second via portion to expose themetal-containing trace and form a full via. When the barrier layer isetched, the metal polymer layer is formed. The metal polymer layer isthen subjected to a nitric acid dip that removes the metal polymerlayer. Once a clean full via is achieved, a contact may be completed by,as known in the art, depositing a conductive material into the via.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention can be more readily ascertained fromthe following description of the invention when read in conjunction withthe accompanying drawings in which:

FIGS. 1-3 are side cross-sectional views of a method of removing residuematerial from a via according to a technique of the present invention;

FIGS. 4-9 are side cross-sectional views of a method of removing residuematerial while forming a via according to another technique of thepresent invention;

FIG. 10 is a side cross-sectional view of a contact formed according toa technique of the present invention; and

FIGS. 11-14 are side cross-sectional views of a prior art via formationprocess according to a known technique.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-3 illustrate one embodiment according to the present inventionfor removing residue layers from a via. It should be understood that thefigures presented in conjunction with this description are not meant tobe actual cross-sectional views of any particular portion of an actualsemiconductor device, but are merely idealized representations which areemployed to more clearly and fully depict the process of the inventionthan would otherwise be possible.

FIG. 1 illustrates a via 106 in an intermediate structure 100 in theproduction of a semiconductor device (similar to FIG. 14) directly afterthe etching of the via 106. This intermediate structure 100 comprises asemiconductor substrate bearing an exposed insulating or dielectriclayer 102, such as an oxide, having a metal-containing trace or pad 104of aluminum, aluminum alloys, titanium, titanium/tungsten alloys,molybdenum, or the like, disposed thereon. The via 106 extends through adielectric layer 108, such as silicon dioxide or the like, and a barrierlayer 112, such as silicon nitride, which are disposed over theinsulating or dielectric layer 102. The sidewalls 114 of the via 106 arecoated with a residue layer 116. As used herein, the term “sidewall” ofa via encompasses both a single, continuous sidewall, such as may definea round or circular via, as well as a plurality of sidewalls defining avia of another cross-section.

The presence of the residue layer 116 is a natural consequence of theetching of the via 106 and generally comprises two distinct layers: anoxide polymer layer 118 and a metal polymer layer 120. As previouslydiscussed, a partial via or first via portion may be selectively etchedthrough an etch mask 122 down through the dielectric layer 108 to thebarrier layer 112 (an etch stop), which results in the oxide polymerlayer 118 and is usually a carbon-fluorine-based, polymer-containingresidue of the dielectric layer 108, coating the sidewalls of thepartial via. The barrier layer 112 may be then etched to create asecond, contiguous via portion and expose the metal-containing trace orpad 104, thereby forming the via 106.

As discussed above, due to thickness variations in the dielectric layer108, the barrier layer 112 is typically over-etched such that the etchwill usually extend through the barrier layer 112 and into themetal-containing trace or pad 104. When the barrier layer 112 andunderlying metal-containing trace or pad 104 are etched, a metal polymerlayer 120 is formed atop the oxide polymer layer 118. The metal polymerlayer 120 usually comprises a carbon-fluorine-based polymer includingmetal etched from the metal-containing trace or pad 104, as well as anymetal components in the barrier layer 112, such as the titanium in atitanium nitride barrier layer 112. Again, as previously discussed, asingle etch could be performed to penetrate dielectric layer 108 andbarrier layer 112 and expose the metal-containing trace or pad 104,which would result in a single residue layer. However, the singleresidue layer would still have an inner portion of the residue layeradjacent the via sidewall 114 containing primarily an oxide polymer anda outer portion adjacent the via 106 containing primarily a metalpolymer.

It has been found by the inventors that a concentrated nitric acid iseffective in removing the metal polymer layer 120 portion of the residuelayer 116, and phosphoric acid is effective in removing the oxidepolymer layer 118 portion of the residue layer 116. However, it has beenfound by the inventors that it was not possible to completely remove allof the residue layer 116 by either phosphoric acid application or nitricacid application alone. It was further found by the inventors thatattempts to completely remove the residue layer 116 by increasing theresidence time in the phosphoric acid results in damage to the barrierlayer 112 and/or the metal-containing trace or pad 104. Furthermore,mixtures of phosphoric acid and nitric acid were also found to beunacceptable for removal of the residue layer 116.

Thus, a two-step cleaning process may be used to substantially removethe entire residue layer 116. The residue layer 116 is first subjectedto a nitric acid dip for about 200 seconds to remove the metal polymerlayer 120 and expose the oxide polymer layer 118, as shown in FIG. 2.The nitric acid dip may preferably contain between about 50% and 100% byweight nitric acid, most preferably about 70% by weight, and preferablyhave a temperature between about 10° C. and 100° C., most preferablyabout 25° C. The duration of the nitric acid dip is preferably betweenabout 10 seconds and 30 minutes, most preferably 200 seconds. However,the duration of the nitric acid dip will depend on the concentration andtemperature of the nitric acid dip.

The oxide polymer layer 118 is then subjected to a 35° C. phosphoricacid solution dip, preferably about a 20:1 ratio (volume of water tovolume of acid) solution, for about 90 seconds, which removes the oxidepolymer layer 118, as shown in FIG. 3, after the etch mask 122 has beenremoved. The phosphoric acid solution dip may be in a concentrationbetween about 200:1 and 1:1 volumetric ratio of water to acid at atemperature of between about 10° and 80° C. The duration of thephosphoric acid solution dip is preferably between about 10 seconds and10 minutes. However, the duration of the phosphoric acid dip will dependon the concentration and temperature of the dip.

In an experiment employing the aforementioned method, nitric acid andphosphoric acid dips were used to clean vias of depths ranging from 0.4to 0.7 microns and having diameters ranging from 0.4 to 1 micron andexhibiting metal polymer layers of approximately 200 Å in thickness andoxide polymer layers of approximately 300 Å in thickness. A nitric aciddip was used at about 70% by weight nitric acid, at about ambient roomtemperature and for a duration of about 200 seconds. A subsequentphosphoric acid dip at about a 20:1 ratio acid to water volume wasemployed at about 35° C. for about 90 seconds. No detectable metalpolymer or oxide polymer remained in the vias after treatment. Thus, anitric acid dip of about 100 seconds was demonstrated to remove about100 Å in thickness of oxide polymer.

It has also been found that the oxide polymer layer 118 can be removedby subjecting the oxide polymer layer 118 to a dip influorine-containing mixtures; for example, components such ashydrofluoric acid (HF) and ammonium fluoride (NH₄F) may be used in lieuof the phosphoric acid solution or mixed with phosphoric acid forremoval of the oxide polymer layer. A preferred concentration for suchfluorine-containing mixtures may range from about 0.01% to about 2%.

As illustrated in FIGS. 4-9, the two-step process may also be effectedduring the formation of a via. Elements common between FIGS. 1-3 and 4-9retain the same numeric designation. FIG. 4 illustrates an intermediatestructure 150 comprising a semiconductor substrate bearing an insulatingor dielectric layer 102 having a metal-containing trace or pad 104formed thereon. A barrier layer 112, such as silicon nitride, extendsover the metal-containing trace or pad 104 and a dielectric layer 108,such as silicon dioxide, is disposed over the barrier layer 112. Asshown in FIG. 5, the dielectric layer 108 is masked with an etch mask122, which is patterned to define the via location. A partial via orfirst via portion 152 is then selectively etched down to the barrierlayer 112 (an etch stop), which results in the oxide polymer layer 118and is usually a carbon-fluorine-based, polymer-containing residue ofthe dielectric layer 108, coating the sidewalls of the partial via 152,as shown in FIG. 6. The oxide polymer layer 118 is then subjected to aphosphoric acid solution dip, preferably about a 20:1 volume ratio ofwater to phosphoric acid at about 35° C. for about 90 seconds, to removethe oxide polymer layer 118, as shown in FIG. 7.

The barrier layer 112 is then etched to form a second via portion andexpose the metal-containing trace or pad 104, thereby forming a full via156, as shown in FIG. 8. When the barrier layer 112 is etched, asdiscussed above, a metal polymer layer 120 is formed, which is usually acarbon-fluorine-based polymer including metal etched from themetal-containing trace or pad 104, as well as any metal components inthe barrier layer 112. The metal polymer layer 120 is then subjected toa nitric acid dip, preferably approximately 70% volume nitric acid forabout 200 seconds, which removes the metal polymer layer 120, as shownin FIG. 9, after the etch mask 122 has been removed.

Once a clean via is achieved, a contact 160 may be completed bydepositing a conductive material 162 into the via, as shown in FIG. 10.The conductive material 162 is preferably a metal, including, but notlimited to, copper, silver, gold, aluminum (preferred), and alloysthereof. However, conductive polymers may be used. The deposition of theconductive material 162 may be effected by methods including, but notlimited to, hot sputter/reflow, ionized plasma, hot pressure fill, aswell as physical vapor deposition and chemical vapor depositioncombinations.

Having thus described in detail preferred embodiments of the presentinvention, it is to be understood that the invention defined by theappended claims is not to be limited by particular details set forth inthe above description as many apparent variations thereof are possiblewithout departing from the spirit or scope thereof.

What is claimed is:
 1. A method of fabricating a contact opening in adielectric layer and a barrier layer for a semiconductor device,comprising: providing a semiconductor substrate having a conductive pad;forming the barrier layer over the semiconductor substrate and theconductive pad; forming the dielectric layer over the barrier layer;forming a first via portion by anisotropic etching through thedielectric layer to expose a portion of the barrier layer thesaid-formation of the first via portion forming an oxide polymer residuewithin the first via portion; applying a phosphoric acid-containingsolution within the first via portion to remove the oxide polymerresidue; forming a second via portion by anisotropic etching through theexposed portion of the barrier layer, the formation of the second viaportion forming a metal polymer residue within the first and second viaportions; and applying a nitric acid-containing solution within thefirst and second via portions to remove the metal polymer residue. 2.The method of claim 1, further comprising applying the nitricacid-containing solution in a concentration of between about 50% and100% by weight.
 3. The method of claim 1, further comprising applyingthe nitric acid-containing solution for a time span of between about 10seconds and 30 minutes.
 4. The method of claim 1, further comprisingapplying the nitric acid-containing solution at a temperature of betweenabout 10° C. and 80° C.
 5. The method of claim 1, further comprisingapplying the phosphoric acid-containing solution in a concentration ofbetween about 200 volumes of water to about 1 volume of phosphoric acidand about 1 volume of water to about 1 volume of phosphoric acid.
 6. Themethod of claim 1, further comprising applying the phosphoricacid-containing solution at a temperature of between about 10° C. and80° C.
 7. The method of claim 1, further comprising applying thephosphoric acid-containing solution for a time span of between about 10seconds and 10 minutes.
 8. The method of claim 1, wherein the phosphoricacid-containing solution further includes a fluorine-containingcomponent.
 9. The method of claim 2, further comprising applying thenitric acid-containing solution in a concentration of about 70% byweight.
 10. The method of claim 3, further comprising applying thenitric acid-containing solution in a time span of about 200 seconds. 11.The method of claim 4, further comprising applying the nitricacid-containing solution at a temperature of about 25° C.
 12. The methodof claim 5, further comprising applying the phosphoric acid-containingsolution in a concentration of about 20 volumes of water to about 1volume of phosphoric acid.
 13. The method of claim 6, further comprisingapplying the phosphoric acid-containing solution at a temperature ofabout 35° C.
 14. The method of claim 7, further comprising applying thephosphoric acid-containing solution for a time span of about 90 seconds.15. The method of claim 8, wherein the fluorine-containing componentincludes hydrofluoric acid.
 16. The method of claim 15, wherein thefluorine-containing component includes ammonium fluoride.
 17. A methodof fabricating a contact opening in a dielectric layer and a barrierlayer for a semiconductor device, comprising: providing a semiconductorsubstrate having a conductive pad; forming the barrier layer over thesemiconductor substrate and the conductive pad; forming the dielectriclayer over the barrier layer; forming a first via portion havingsubstantially parallel sidewalls through the dielectric layer to exposea portion of the barrier layer, the formation of the first via portionforming an oxide polymer residue within the first via portion; applyinga solution including a fluorine-containing component within the firstvia portion to remove the oxide polymer residue; forming a second viaportion having substantially parallel sidewalls contiguous with thesubstantially parallel sidewalls of the first via portion through theexposed portion of the barrier layer the said-formation of the secondvia portion forming a metal polymer residue within the first and secondvia portions; and applying nitric acid within the first and second viaportions to remove the metal polymer residue.
 18. The method of claim17, further comprising applying the nitric acid in a concentration ofbetween about 50% and 100% by weight.
 19. The method of claim 17,further comprising applying the nitric acid for a time span of betweenabout 10 seconds and 30 minutes.
 20. The method of claim 17, furthercomprising applying the nitric acid at a temperature of between about10° C. and 80° C.
 21. The method of claim 17, wherein thefluorine-containing component further comprises phosphoric acid.
 22. Themethod of claim 17, wherein the fluorine-containing component includeshydrofluoric acid.
 23. The method of claim 17, wherein thefluorine-containing component includes ammonium fluoride.
 24. The methodof claim 18, further comprising applying the nitric acid in aconcentration of about 70% by weight.
 25. The method of claim 19,further comprising applying the nitric acid in a time span of about 200seconds.
 26. The method of claim 20, further comprising applying thenitric acid at a temperature of about 25° C.
 27. The method of claim 21,further comprising applying the phosphoric acid in a concentration ofbetween about 200 volumes of water to about 1 volume of phosphoric acidand about 1 volume of water to about 1 volume of phosphoric acid. 28.The method of claim 27, further comprising applying the phosphoric acidin a concentration of about 20 volumes of water to about 1 volume ofphosphoric acid.
 29. A method of fabricating a contact opening in adielectric layer and a barrier layer for a semiconductor device,comprising: providing a semiconductor substrate having a metal trace;forming the barrier layer over the semiconductor substrate and the metaltrace; forming the dielectric layer over the barrier layer; forming afirst via portion by anisotropic etching through the dielectric layer toexpose a portion of the barrier layer the formation of the first viaportion forming an oxide polymer residue within the first via portion;forming a second via portion by anisotropic etching through the exposedportion of the barrier layer, the formation of said-the-second viaportion exposing the metal trace and forming a metal polymer residue;applying nitric acid within the first and second via portions to removethe metal polymer residue; and applying a solution including afluorine-containing component within the first via portion, afterapplying the nitric acid, to remove the oxide polymer residue.
 30. Themethod of claim 29, wherein providing the semiconductor substrate havingthe metal trace comprises providing a semiconductor substrate having atrace including a metal selected from the group consisting of aluminum,aluminum alloy, titanium, titanium alloy, and molybdenum.
 31. The methodof claim 29, further comprising applying the nitric acid in aconcentration of between about 50% and 100% by weight.
 32. The method ofclaim 29, further comprising applying the nitric acid for a time span ofbetween about 10 seconds and 30 minutes.
 33. The method of claim 29,further comprising applying the nitric acid at a temperature of betweenabout 10° C. and 80° C.
 34. The method of claim 29, wherein thefluorine-containing component further comprises phosphoric acid.
 35. Themethod of claim 29, wherein the fluorine-containing component includeshydrofluoric acid.
 36. The method of claim 29, wherein thefluorine-containing component includes ammonium fluoride.
 37. The methodof claim 31, further comprising applying the nitric acid in aconcentration of about 70% by weight.
 38. The method of claim 32,further comprising applying the nitric acid in a time span of about 200seconds.
 39. The method of claim 33, further comprising applying thenitric acid at a temperature of about 25° C.
 40. The method of claim 34,further comprising applying the phosphoric acid in a concentration ofbetween about 200 volumes of water to about 1 volume of phosphoric acidand about 1 volume of water to about 1 volume of phosphoric acid. 41.The method of claim 40, further comprising applying the phosphoric acidin a concentration of about 20 volumes of water to about 1 volume ofphosphoric acid.
 42. A method of fabricating a contact opening in adielectric layer and a barrier layer for a semiconductor device,comprising: providing a semiconductor substrate having a metal trace;forming the barrier layer over the semiconductor substrate and the metaltrace; forming the dielectric layer over the barrier layer; forming afirst via portion defined by substantially parallel sidewall portionsthrough the dielectric layer to expose a portion of the barrier layer,the formation of the first via portion forming an oxide polymer residuewithin the first via portion; applying a solution including afluorine-containing component within the first via portion to remove theoxide polymer residue; forming a second via portion defined bysubstantially parallel sidewall portions contiguous with the sidewallportions of the first via portion through the exposed portion of thebarrier layer, the formation of the second via portion exposing themetal trace and forming a metal polymer residue within the first andsecond via portions; and applying a nitric acid-containing solution,independent of applying the fluorine-containing component, within thefirst and second via portions to remove the metal polymer residue. 43.The method of claim 42, wherein providing the semiconductor substratehaving the metal trace comprises providing a semiconductor substratehaving a trace including a metal selected from the group consisting ofaluminum, aluminum alloy, titanium, titanium alloy, and molybdenum. 44.The method of claim 42, further comprising applying the nitricacid-containing solution in a concentration of between about 50% and100% by weight.
 45. The method of claim 42, further comprising applyingthe nitric acid-containing solution for a time span of between about 10seconds and 30 minutes.
 46. The method of claim 42, further comprisingapplying the nitric acid-containing solution at a temperature of betweenabout 10° C. and 80° C.
 47. The method of claim 42, wherein thefluorine-containing component further comprises phosphoric acid.
 48. Themethod of claim 42, wherein the fluorine-containing component includeshydrofluoric acid.
 49. The method of claim 42, wherein thefluorine-containing component includes ammonium fluoride.
 50. The methodof claim 44, further comprising applying the nitric acid-containingsolution in a concentration of about 70% by weight.
 51. The method ofclaim 45, further comprising applying the nitric acid-containingsolution in a time span of about 200 seconds.
 52. The method of claim46, further comprising applying the nitric acid-containing solution at atemperature of about 25° C.
 53. The method of claim 47, furthercomprising applying the phosphoric acid in a concentration of betweenabout 200 volumes of water to about 1 volume of phosphoric acid andabout 1 volume of water to about 1 volume of phosphoric acid.
 54. Themethod of claim 53, further comprising applying the phosphoric acid in aconcentration of about 20 volumes of water to about 1 volume ofphosphoric acid.